Definition of Vomitus

Vomitus: Matter from the stomach that has come up into and may be ejected beyond the mouth, due to the act of vomiting.

When vomitus is reddish or the color of coffee grounds, it may mean there is serious internal bleeding. The reddish color may herald fresh blood and dark blood may betoken blood that has been digested.

Vomitus and vomit are synonymous as nouns although only vomit is used as a verb. The act of vomiting is also called emesis.
From the Indo-European root wem- (to vomit), the source of the words such as emetic and wamble (to feel nauseated).